1. Field of Invention
This invention relates to a biochip for testing such substances as DNA, RNA or protein; and, more particularly, to a biochip that is safe and reduces cost of testing.
2. Description of the Prior Art
A biochip, such as a DNA chip, comprises several thousand to several hundred thousand types of known DNA segments, also referred to as DNA probes, deposited in a plurality of arrays on a substrate. If a solution containing an unknown DNA segment, also referred to as a DNA target, is caused to flow onto such a DNA chip, DNA segments of the same type combine with each other. This property is utilized so that a DNA probe, wherein such combination has taken place, is examined using a biochip reader, and thus, the sequence of the DNA target, for example, is determined.
FIG. 1 shows an example of hybridization seen in a biochip, wherein six DNA probes DN01, DN02, DN03, DN04, DN05 and DN06 are deposited in a plurality of arrays on a substrate SB01, thus forming a DNA chip. A DNA target UNO1 is previously marked with a fluorescent marker LM01. When hybridized to the DNA chip, the DNA target combines with a DNA probe whose sequence is complementary. For example, the DNA target UNO1 combines with DNA probe DN01, as indicated by CB01. Using a biochip reader, excitation light is irradiated at the DNA chip, thus hybridized, in order to detect fluorescent light produced at the fluorescent marker. Hence, it is possible to know which of the DNA probes the DNA target has combined with. For example, in an image SI01 resulting from scanning a DNA chip, fluorescent light is observed at the spot LD01 whereat the DNA combination CB01 was produced.
FIG. 2 shows a DNA chip as the biochip, wherein the biochip comprises a substrate 1, on which known DNA segments are deposited in a plurality of arrays (referred to as xe2x80x9csubstrate 1xe2x80x9d); a cartridge 2 wherein the substrate 1 is housed and to which a solution containing a DNA target previously marked with a fluorescent marker is introduced; and an inlet opening 3 formed on cartridge 2 through which a solution is introduced. Cartridge 2 comprises a material which is permeable to both excitation light and fluorescent light produced thereby at the marker. Cells CL11, CL12, CL13, CL14, CL15 and CL16, in each of which a plurality of DNA probes of the same type are placed, are deposited in arrays on substrate 1.
The method of testing DNA or other substance using the biochip of FIG. 2 is described with reference to FIGS. 3 and 4, wherein FIG. 3 shows an example of introducing solution into cartridge 2, and FIG. 4 shows art example of scanning a hybridized DNA chip using a biochip reader to determine the sequence of target DNA, for example. FIG. 3 shows components 1 to 3 which are the same as those in FIG. 2.
In a first step, blood is collected using a syringe from a person being tested. A solution that was preprocessed is then introduced through an inlet opening 3 into cartridge 2. Solution infusion means or device 4, such as a pipette, is loaded with a preprocessed solution 5. The tip of solution infusion device 4 is inserted in inlet opening 3 and solution 5, inside the device 4, is injected into cartridge 2. The preprocessing refers to a series of processes wherein lymphocytes are separated from the collected blood, and then DNA is extracted from the separated lymphocytes, and finally, the extracted DNA is marked with a fluorescent marker.
In a second step, substrate 1 is soaked with solution introduced into cartridge 2 to allow a DNA target in the solution to hybridize with DNA probes placed in each cell on substrate 1.
In a final step, as shown in FIG. 4, hybridized substrate 1 is scanned using a biochip reader 50 so that, for example, the sequence of the DNA target is determined.
In FIG. 4, components 1 to 3 and cells CL11,CL12, and CL13 are similarly denoted as in FIG. 3. In addition, light emitted from a light source 6, such as a laser light source, is reflected by a dichroic mirror 7, as excitation light and focused through an objective lens 8 onto cells on substrate 1. For example, excitation light is focused onto cell CL12 in FIG. 4. Fluorescent light produced at cell CL12 on substrate 1 becomes parallel light at it travels through objective lens 8 and is projected onto dichroic mirror 7. The fluorescent light, thus projected, is transmitted through dichroic mirror 7. The fluorescent light thus transmitted then travels through a filter 9 and is condensed onto an optical detector 11 by a lens 10.
The spots, whereon excitation light is focused, are scanned by a drive means (not shown). For example, cartridge 2 or biochip reader 50 itself is scanned so that excitation light is irradiated at the remaining cells CL11 and CL13 on substrate 1. Hence, it is possible to determine the sequence of a-DNA target by identifying the position of a cell on substrate 1 where fluorescence takes place.
Recently, however, test samples, such as blood, have been found to be contaminated with a virus, such as HIV. Hence, there is a growing tendency, for safety reasons, to not recycle various medical devices, such as syringes, for cleaning or sterilization. Instead, disposable devices are preferred. In contrast, the method of introducing a solution, such as shown in FIG. 3, involves the risk of the human operator or testor becoming infected by a virus, such as HIV, as result of accidental contact with the solution. This risk is due to the transfer of the solution from the solution infusion device 4, or the like to cartridge 2.
Another problem is that the cost of testing is substantial since more than one type of medical equipment or device must be disposed of, including syringes, devices and appliances used for preprocessing purposes, solution infusion devices, DNA chips, etc.
Accordingly, an object of the invention is to overcome the aforementioned and other deficiencies, disadvantages, and problems of the prior art.
Another object is to provide a biochip which is extremely safe and enables great reduction in cost of testing.
The foregoing and other objects are attained in the invention, which encompasses a biochip collection means for retaining collected blood; preprocessing means for deriving a target from the collected blood; and substrate means on which probes are deposited in arrays with the opening thereto being air tight.